If it's not specified in the Settings menu or in the Help section, you can switch between windows in the application using the standard keys. To switch between windows, press Ctrl + TAB. The Alt + Tab switches opened Windows outside the program, while the Control + Tab is for the active application.
I also recommend checking the built-in Help documentation as well to find more about various settings offered by the application.

Video and screenshots

Review

Subtitle Edit is a free (open source) editor for video subtitles - a subtitle editor. With Subtitle Edit you can easily adjust a subtitle if it is out of sync with the video and much more. Create/adjust/sync/translate subtitle lines, Convert between SubRib, MicroDVD, Substation Alpha, SAMI, youtube sbv, and many more. Un can use Auto Translation via Google translate or Microsoft Bing Translate.